Motorola STARLINE SERIES Instructions d'exploitation télécharger pdf (Page 43)

BLE*/* Installation and Operation Manual

Section 6

Operating Tips

This section describes using amplifiers in lower frequency systems and in lower gain systems.

Using Amplifiers in Lower Frequency Systems

When using the BLE*/* in 750 MHz or 550 MHz systems, you must consider the best method for

handling the reduced bandwidth and channel-loading requirement. The following information

helps you determine the best approach.

For distribution systems designed and installed as 870 MHz systems, but carrying a reduced

channel load, there are no further concerns. You can add or remove channels at your discretion.

If the system operates with ADUs, the pilot channel cannot be disturbed. Reduced channel

loading improves distortion.

For lower-frequency systems, such as 750 MHz or 550 MHz, you will need to take into account

the reduced gain from 870 MHz. Due to the amplifier tilt, there will be some loss in gain from

the published operational specification at 870 MHz. For example, a 32 dB 870 MHz BLE with 12

dB of tilt will lose approximately 1.5 dB of gain to 750 MHz, resulting in approximately 30.5 dB

of gain at 750 MHz. If tilt needs to be adjusted, you may accommodate by changing the forward

equalizer (SFE) value. Also, to avoid any additional loss in gain, it is optimal to use the

equalizers that match the system frequency. For a 750 MHz system, the SFE-75-*s are the best

choice, even in an 870 MHz amplifier. Note also, that the equalizer cuts off at the frequency

value for which it is designed. For example, an SFE-75-* cuts off frequencies above 750 MHz.

Therefore, if you have an 870 MHz system and need the equalizer to perform to 870 MHz, you

must use an SFE-87-*.

Using Amplifiers in Lower Gain Systems

There are two pad facilities in the forward path: (1) the pad location (JXP-IN) at the input to the

amplifier, and (2) the midstage pad (JXP-MID) located between the pre-amplifier and the output

hybrid.

The input pad (JXP-IN) is normally changed to accommodate excessive input levels. When

operating at the same output levels, a BLE*/* with an input pad has the same carrier-to-noise

(c/n) and distortion performance as a BLE*/* without the input pad. Because it only attenuates

excess signal, it has no effect on the overall performance of the BLE*/*.

If necessary, to achieve the gain specification, you can use the midstage pad (JXP-MID) to

reduce the gain of the BLE*/*. However, this will affect amplifier performance. Midstage

padding has minimal impact on the noise figure, therefore, carrier-to-noise performance is

maintained. When operating at the same output levels, the midstage pad forces the

pre-amplifier to operate at a higher output level, thereby degrading station distortion

performance. Due to the superior distortion performance provided by the latest E-GaAs BLEs,

this should not be a major concern assuming the pad value is reasonable.

It is recommended that you contact Motorola’s TRC or your account representative for specific

information regarding use of the midstage pads.

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Motorola STARLINE SERIES Instructions d'exploitation Page 43